The present invention relates to a field effect transistor, and more particularly to an insulated gate type field effect transistor having a short channel length.
Recently, the channel length between the source and drain regions of the insulated gate type field effect transistor has become short, as short as 1 .mu.m or less, for realizing high speed operation by reducing the capacity between the gate electrode and the channel region. However, such a short channel transistor inevitably has applied therein a high electric field along the channel direction, and therefore, a carrier temperature, that is, an electron temperature in an N-channel type transistor in the channel region rises to an unexpectedly high level. In this case, the carrier speed becomes saturated because of a reduction of carrier mobility by the high temperature condition mentioned above. Then, the desired amount of drain current which would be expected from the mobility of the carrier at a low electric field intensity cannot be obtained. Therefore, in the prior art, the effect of speeding up of the short channel transistor is due to the reduction of the gate capacity alone, and any increase in the drain current does not contribute. Further, the carrier of the high temperature under the high electric field intensity is injected into the gate insulating film, and causes the deterioration of the device.